As long as you use a name brand like PPG or BASF or for Black DuPont is good , the fading depends on the "Clearcoat" many shops use a cheaper clear , if you use PPG or whatever brand keep it all the same so it will covered under warranty (most Paint companies do that now) if you are going to color sand make sure the painter puts on enough clear because sanding and polishing removes a bit of the top coat / clearcoat , I would be more worried about matching the original "Orange Peel" look that most Cars have today , you should not have a problem , if it were a white pearl or a metallic that is a litle harder to perform a good match.